(a) Field of the Invention
The present invention relates to a liquid crystal display, and in particular, to a liquid crystal display with multi-line inversion which reverses polarity of applied voltages every two or more rows for preventing the deterioration of liquid crystal. The present invention relates to a liquid crystal display for improving uniformity of image quality of pixels in the rows having reversed polarity.
(b) Description of the Related Art
Recently, displays used for personal computers or TVs are required to be light and slim, and flat panel displays such as liquid crystal displays (LCD) instead of cathode ray tubes are developed and put to practical use for satisfying such a requirement.
The LCD includes a panel including a pixel matrix pattern and another panel opposite thereto. A liquid crystal (LC) having dielectric anisotropy is interposed between the panels. An electric field is generated between the panels. Desired images are displayed by adjusting the field strength to control the transmittance of light passing through the panels.
The LCD receives n-bit red, green, blue (RGB) data from an external graphics source. A timing controller of the LCD data-transforms the RGB data and a data driving integrated circuit (IC) selects gray voltages corresponding to the RGB data. The selected gray voltages are applied to the pixels of the panels to perform display. The gray voltages are DC components. Long-time application of gray voltages with a single polarity to the pixels on the panels deteriorates the liquid crystal in the pixels. This kind of the deterioration of the liquid crystal can be prevented by inversion which reverses the polarity every pixel, every pixel line (or row), or every frame. The present invention relates to an LCD in multi-line inversion, which reverses the polarity of the applied voltages every two or more lines.
FIG. 1 shows waveforms of a data signal and a load signal LOAD in an exemplary multi-line inversion, i.e., a double-line inversion reversing the polarity every two lines.
The data signal shown in FIG. 1 represents display information by its voltage level and is outputted from a data driving IC to be applied to pixels of an LCD panel. The load signal LOAD controls a timing of data signal application from the data driving IC to the LC panels. A duration between two adjacent dotted lines is called a horizontal period (abbreviated as “1H”) and the character “N” means that the data signal is applied to the N-th pixel row in the LCD panel. For example, upon receipt of a pulse of the load signal LOAD, the data driving IC of the LCD outputs the data signal to a corresponding data line on the LC panel.
As shown in FIG. 1, the polarity of the data signal applied to the pixel on the LC panel is reversed every two pixel rows with respect to a common voltage Vcom.
The LCD in the multi-line inversion has a problem that the pixels in the rows with reversed polarity are not sufficiently charged. In the example shown in FIG. 1, the amount of charges stored in a pixel in the N-th row are different that stored in a pixels in the (N+1)-th row even if both the pixels represent equal gray level. Since a predetermined transition time for the voltage of the pixel in the N-th row to reach a target level due to the polarity inversion for the N-th row is required, the stored charges in the pixel in the N-th row and the pixel in the (N+1)-th row is different. The difference in the stored charges causes the difference in the luminance, thereby deteriorating display characteristics. For example, the pixel in the N-th row experiencing the polarity inversion is brighter than the pixel in the (N+1)-th row, which has an equal gray level, for a normally white mode LCD since the amount of the stored charges in the pixels of the N-th row is smaller than that the pixel of the (N+1)-th row. As a result, an LCD with the conventional multi-line inversion has a problem of luminance difference between the pixels in the rows experiencing the polarity inversion and the pixels in the other rows.